Acrylic-based polymers have been broadly used as adhesives, coatings and sealants since they are relatively low in cost, adhere well to a variety of different surfaces and, if necessary, can be formulated to build adhesion to a surface. The disadvantages of acrylic-based polymers include poor high temperature performance, poor low temperature performance, inability to adhere to substrates with low surface energies and the potential to build excessive adhesion to substrates with high surfaces energies.
Silicone-based polymers exhibit both good high and low temperature performance as adhesives, coatings and sealants. Silicone-based polymers have excellent chemical inertness, electrical insulating properties, biocompatibility, and the ability to adhere to low surface energy substrates. A primary disadvantage of silicone-based polymers is their high cost compared to other types of technologies. Other limitations include lower tack and limited adhesion build, when necessary, in comparison to acrylic-based polymers.
While individual silicone adhesive and acrylic polymer have distinct advantages, and although they may be physically blended to form a hybrid polymer system, the blend is thermodynamically unstable and ultimately leads to macroscopic phase separation and change in the blend properties over time.
An attempt to overcome this incompatibility has been addressed in WO 2007/145996, which forms an acrylic grafted silicone adhesive by a complex process. However, this complex process makes removal of residual monomer difficult and the level of crosslinking cannot be well controlled. If any unreacted silicone and acrylic components remain, this unreacted components lead to phase separation over time, even if the rest of components are covalently grafted.
Covalent grafting of silicone and acrylics may be formed by reacting a silicone polymer and an acrylic polymer, however, a silicone resin is necessary to form a hybrid polymer system. The resultant hybrid polymer system forms silicone resin as the center domain and silicone polymer and acrylics are attached to that domain. Hence, the resultant hybrid polymer system requires the silicone resin as the center domain to form a lattice-type polymer.
There is a need in the art for adhesives, coatings and sealants that exhibit the advantages of both acrylic- and silicone-based technologies without the disadvantages inherent in the prior art. This invention addresses this need.